I have made my observation about handling customers in my topic.
Here about external meatal atresia:
Yes, reconstructions can be done. There are numerous authors who made their surgical observation but is is not always
easy to do. You have to satisfy certain criteria, anathomical at first place.
Maybe you could explore some options for your son.
According to your words, you have problem with middle ear also but perhaps it is possible to create external opening just to add little bit of air conducted part of transmitted sound in your audiogram. Alone, it could be not enough but with some device...
Also, why they proposed to you BB and not Vibrant Soundbridge? Is your middle ear heavy malformed?
There is possibility to put VSB on fenestra ovalis - entry gate to cochlea (inner ear). Theoretically, this should be the best possible transmitted sound without loosing sound quality because of destortion at all.